As a successor to the flash memory, a resistive memory device including a variable resistance element as a memory element has recently drawn attention. Here, the resistive memory device shall include several kinds of devices including resistive RAM (ReRAM) in a narrow sense, and the phase change RAM (PCRAM). The ReRAM includes, as the recording layer, a transition metal oxide and stores its resistance state in a non-volatile manner. The PCRAM includes, as the recording layer, a material such as chalcogenide and uses the resistance information of its crystal state (conductor) and amorphous state (insulator).
The resistive memory device is classified into a bipolar type and a unipolar type. The bipolar resistive memory device sets the high resistance state and the low resistance state by switching the polarity of the applied voltage. In contrast, the unipolar resistive memory device sets the high resistance state and the low resistance state by controlling the applied voltage value and the voltage application time without switching the polarity of the voltage.